Last weekend, my husband and I have replaced the particle board covered in paper railing all the way around the inside. The previous railing was in terrible shape. Our repair job isn't perfect, but is still much better than the "before." We then gave a light stain and polyethylened before installation. To make installation easier, I used an ice pick through the old rail to mark the new holes to drill. Oh, one of our issues is the railings had a lip on it, so we tacked two different pieces together.

https://imgur.com/gallery/C7u6W

that looks very nice!